Design And Development Of High Temperature Superconducting Multi-band Filter

Design and produce filters that have good performance by High-temperature superconductivity material YBa Cu O, which the surface resistance is 1000~3000 times lower than traditional Cu in rf-microwave frequences. Therefore high-pole filters can be made, the insertion loss can be controlled in a low level(usually less than 0.5d B). High-temperature superconductivity(HTS) filter has a very high suppression outside the band, and the frequency selection window is close to the rectangular, saving the transition bandwidth. Using HTS filter on the convention rf front-end receving system, obviously improve its sensitivity in the base station, expand coverage area, enhance inhibition of interference signal, and eliminate the mutual modulation effect. Through putting HTS filter on the first place in the receiver, the LNA is effectively protected, avoiding the impact of strong signal saturation, which don’t increase the system’s noise factor. So HTS filter has a broad application prospect in civilian communication, police cluster communication, military communication, radar precision guidance and ship navigation.Because of all communication frequency are nearly all in rf-microwave frequency, together with the update of exisiting communication protocal and many new protocal are put forward, the spectrum resource is becoming more and more tight. The protocal composed by different frequency is intervalled other communication frequency. Combination of band-pass filters will bring a heavy burden for the receiver equipment, increasing its volume and the difficult of demodulation. If on a chip can achieve multiple frequencies, it will reduce the loss and volume effectively, realizing the miniaturization and saving cost.In this paper, considering the frequency issues and the advantage of HTS filter, design and implement two multi-band HTS filter. At first, design a dual-band filter, which it adopts the traditional cascade structure. In accordance with requirements of indicator respective, band-pass and stop circuit are designed separately and finally they are connected. In the end, The filter film is produced on the La Al O3 substrate, and test it under low temperature environment. Secondly a tri-band filter is achieved. Through introducing strong crossover coupling between an-adjacent resonator on the band-pass filter, the zeros are realized in the passband, so the stopband generating. It gives the optimization method of coupling matrix parameters, and the electromagnetic field simulation softwave building circuit is also described.This article achieve the dual-band and tri-band filters by using HTS material. Through simulating test, the two filters show a excellent character, which prove the feasibility of using the above method. The insertion loss of dual-band is better 0.2d B, and there is a parasite transmiss zeros in the low frequency position, strengthening the suppression in the stop band.